Field of the Invention
The present invention relates to an internal-combustion-engine electronic control system and particularly to an electronic control system that controls an internal-combustion-engine ignition device.
Description of the Related Art
As is well known, in an internal-combustion-engine ignition device, for example, in the case where an ignition signal is inputted for a time longer than a predetermined time, in the case where an electronic component included in the ignition device overheats, or in the case where an excessive current flowing in an ignition coil is detected, it is required to forcibly shut off the primary current of the ignition coil at a timing different from the regular ignition timing so as to protect the ignition device.
However, in the case where the primary current of an ignition coil is forcibly shut off at a timing different from the regular ignition timing, it is required to softly shut off the primary current of an ignition coil in order to prevent a high voltage, which is high enough to cause a spark discharge in the ignition plug, from being generated across the secondary winding of the ignition coil; additionally, in order to suppress heat generation in an electronic component as much as possible, the soft shutoff operation needs to be implemented in a minimum time.
To date, there has been disclosed an internal-combustion-engine ignition device where there are included a current limiting circuit that limits a primary current flowing in an ignition coil, a timer circuit that serves as an abnormality detection means, and a detection circuit that detects abnormal heating, and when any one of these circuits detects an abnormality, the primary current of the ignition coil is softly shut off in a time between 17 [ms] and 135 [ms] (for example, refer to Patent Document 1).
Patent Document 1: JP-A-2008-45514
The conventional system disclosed in Patent Document 1 is provided with a circuit that softly shuts off the primary current of an ignition coil in a time between 17 [ms] and 135 [ms] when an abnormality in an ignition device is detected; however, neither the inductance and the impedance of an ignition coil nor the characteristics of an insulated-gate bipolar transistor is taken into account. As a result, there has been a problem that the time of soft shutoff varies depending on these values, the characteristics, the limiting value for the primary current of an ignition coil, or the like.